Automatic regulation of light falling on deformable cathode-ray tube screen



June 17, 1952 E. F. FISCHER AUTOMATIC REGULATION oE LIGHT EALLTNG oN DEEURMABLE cATHoDE-RAT TUBE SCREEN 2 SEETS-EET l Filed Dec. 29, 1947 O 4| 2 4 .a/./ 4 9 /f//f/H 2 Il 5 O G 2 Il 9 95 m 14--- l l E #Iliff/f1-1 2 lllllllll Il f l l l I I l l l l f l l l l l Il \f ||||||||||||||NMMMI'NNHNHHHHHUHHnununu MIJIIIHHN, ,l \m\1|lun n... l/ l l l l l l l l l l l l l I l l l l I l l l l l l ,l Q 1)/ W 3 jllllllllllll INVENTOR. Ernst Friedrich Fischer ATTORNEY June 17, 1952 E. F. FISCHER 2,600,397

AUTOMATIC REGULATION OF LIGHT FALLING ON DEFORMABLE CATHODE-RAY TUBE SCREEN A INVENTOR. Erni?? Friedrich Fischer ATTORNEY Patented June 17, :1952

i 2,600,397 'AUTDMATICRGULATION OF LIGHT ING.. jON, DEFORMABIJ'E l TUBE-SCREEN cATHoDEf-RAY Friedrichliischer, Zuricln-*Switzverland v -npiiifineceniper 29, 1947,'7se'riamo-i'19432'26 In SwitzerlandvDecember-m-1939 section 14, lPublimlaw 69o, August 3,1946 l Patent expires December 9, 17959 2' Claims. (Cl. 1781-75) This invention relates'lto'an im'p'rovementI in, or'mo'dication of, the'inventindescribed and tclaimed infmy patent No. v2',391,450,dated December 25,1945. I a 'vvi'ui thein'ethd' or, and apparatus for; reproducing atelevisionpicture"with a 'cathode ray V'tube and separate light source as described in the .said` patent, the light'of this light source isfso controlledby' an'fopticallayer which is deform- A'able bythe oathode'ray, that'vvhenra picture is present it is'projected by different lens systems fonmto'rthefprjeetion screen, whereas, otherwise, f"\`i}hnfthe'layr is ot deform'eiitis 'projected on to" a shutter for iaphragnr 'which `prevents Y the entire light 'from reaching the' projectionl screen. Thus', 'when the layer is not deformed, the projection screen remains absolutely dark, whereas when the'laye'r is deformed, the' light reaches the 'piiojeetion screenby passing by `the diaphragm. However, it isknown in the art thatthe usual vlens sy'sterns do not function in an ideal manner, butl 'produce' scattered light to a Agreater orless degree. Consequently even with the subject matter of the inventionV of the patent, in whicheven several lenssystems are employed, it is not pos- ,"vsible to eliminate scattered light which, even "when 'the'diaphragm is not deformed, reachesthe projection 'screen past the diaphragm and imparts to the latter a certain basic brightness, Whichcannot be reduced.

Since, as irsuknowrn the scattered light bears a definite relationship to the stream of light sup- 1plied by the light source, the basic brightness produced by the scattered light'isdirectly proportional tothe stream of light or brightness of thel light source. As is also known, this basic brightessllrhirn Prewncthebees parts f the ric- ;ilre, @om @peering @s ,complely black paift 0n n the projection screen. Ahas a detrimental effecten of contrast of aV pictnre only when the ,rii-Qfthe brightness.Qfihebrghtest parte; 0f the Dliiile treibe brightness ofthe darkest verts falls Vbelovva denite amount. vAccording to tests, thisratio should amount to at least 100 in order to obtain a picture with satisfactory graduations of brightness. The quality 'f a picture is thus not dependent uponthe Vbasic'brightness infitself, 'but upon the said ratio, which is referred to as the range of brightness of the picture.

Now, with the device according to the aforesaid patent, the disadvantage exists that in the projection of pictures with poor lights, i. e. of pictures having a small average brightness, the constant basic brightness always appears in a disturbing manner.

lf, for: example; the range of 'brightness'of`-the pictureamo'unts to just 10o wiui the'meaimfdformed to its'maximum extent,vvhich is obtainable with the lens system whichis customary -at vthe present time, and thus a good quality picture is lformed, then "Withi a picturehavingari`` average brightnesswhich Vonly amounts to'atenthfof this,

the' rangeiof brightnessdrol's tothe inadmissible small amount 10, inl consequence ofthebasic brightness remaining constant.

'The object" of the presentinvention, therefore, isV to provide' a ,method off-fand" "appara'tils?v ifor,

` eliminating"thesedisavantages A'cee-ming to 'the inversin;there@ stream of the separate lights"sourcefisoontolled "ncecrdince""withV the've'rage picture 'brigrit ess of the individual picturesj wlrereb'ya compensation is simultaneously "and automatically obtained by increasedintensiiicationof the'p'icture. l l g l The apparatus for carrying this vmethod into 'effect includes a device for determiningtheavrsimultaneous increase in the A'intensi'cation "of the picture, the latter'A appears' on the projection screen 'with the correct brightness 'values "despite the reduc'edlight stream. This is to be explained y by the ffact that the increased intensification Of the picture signal results in an increasedldeformation of the medium, whereby' in return more lightfreaches the''projecticn'iscreen.l

As Will be readily understood, the brightnessfof `a picture point on the projection screenisjdependent upon the product of light stream multiplied by deformation of the layerl atfthe'eorresponding place, for the product ofligh't stream multiplied by intensification. As the individual factors ofthe product are correspondingly'vaiii'ed, the brightness of the picture point 'cannev'rtliethe scattered light declines c'6resporiding"tolthe reduction of the light stream.

'The determination yof the average-picture brightness can take place in linown manner by optical or electrical means, for example, by a photo-cell or by determining the average picture signal potential.

In lm scanners, the photo-cell can be arranged directly at the film frame just. to be scanned or even some frames in front. By

means of the latter arrangement, the result is obtained that the average brightness is already registered a definite time in advance, so that no delay can occur in the control of the light source and of the intensification.

Furthermore, there is no difficulty in infiuencing an intensifier and a restricting device for the light stream with this value found in such a manner. The influencing can be effected by hand or automatically. It is simplest to Yuse the control amplifier or intensifier already described in the above-named patent as the intensifier. Obviously, the cathode ray tube itself can be influenced in such a manner that the average ray current has a definite ratio to the average picture brightness. Y

Various devices and methods can be employed for restricting the light stream or current. For example, the current strength of the light source and thus its brightness can be varied or, with a xed brightness of the light source, the light current can be varied by inserting diaphragms in the path of light or filters of stronger or weaker absorptive power.

Further, control devices can be provided in the light current which contain means for polarisation, production of double refraction and for analysis. As is known, light currents can be varied with the aid of such devices, by for example, the polariser and analyser being rotated relatively to one another or with respect to the double-refracting means, or by the magnitude of the double refraction being influenced, which, with many substances, can be obtained with the aid of an electric potential.

Finally, it is also possible to provide. in the light current, variable diffracting or refracting means for controlling the light current.

In the accompanying drawing, there is diagrammatically shown in Figs. 1 and 2, by way of example, an arrangement for the control of the light stream with, at the same time, corresponding amplification of the television signal.

The drawing is based on Fig. 4 of my abovementioned patent. For a better understanding of the invention the reference numerals of the said Fig. 4 of the patent have been retained.

A diaphragm 40, which is adjustable by an electromagnet 4|, is arranged in the light stream being emitted by the light source l0. 43 is an I electrical amplifier which, with known means, forms the average value of the television signal arriving through the leads 44. In accordance with this average value, the magnet 4| and thus the diaphragm 40 are, on the one hand, influenced through the leads 42 whereas, on the other hand, in accordance with this average value, a larger or smaller television signal is supplied to the final amplifier 1. Corresponding to the basic idea of the invention, when the electrical picture signal has a large average value. a small signal potential must be supplied to the final amplifier and the light stream must be correspondingly increased, and vice versa.

Fig. 2 represents diagrammatically how the.

average brightness value of a picture is ascertained directly at the iilm scanner. The film 41 is illuminated by a light source 45 through a lens 46, and a photocell 48 is arranged behind the film 41. The photocell current corresponding to the average picture brightness reaches a known control amplifier 5U through the leads 49, the amplifier again influencing the magnet 4I and thus the diaphragm 40 through leads 42. Furthermore, through leads 52, the'v television amplifier 5l to which the television signal is conveyed through leads 44 is inuenced in such a manner that the final amplifier '1' receives a larger or smaller television signal. The manner of operation of this embodiment is otherwise the same as that according to Fig. 1. f

For the sake of simplicity, the parts not essential for the device for varying the light stream according to the television signal are only represented in dotted lines.

Having now particularly described and ascertained the nature of my said invention, and in what mannner the same is to be performed, I declare that what I claim is:

l. A television receiver comprising a cathode ray tube, a separate source of light, a deformable optical layer arranged to be swept by the cathode ray, an optical system for projecting the light beam from said source of light onto a screen by way of said deformable layer, the cathode ray acting to deform the optical layer and thereby to modulate the light beam pursuant to a received television signal, a diaphragm arranged to block the passage of light to the screen when the television signal is zero, and mechanism for eliminating the contrast-reducing effects of stray light projected from the optical layer onto the screen past the diaphragm even when the television signal is zero, and comprising means for determining the average picture brightness of the individual pictures, a device responsive to said brightness-determining means for controlling the light stream for reducing the intensity of such stream when the average brightness falls, and mechanism likewise responsive to said brightness-determining means for simultaneously increasing the amplitude of the picture signal received by the cathode ray tube.

2. Apparatus as defined in claim l, wherein the device for controlling the intensity of the light stream comprises a movable diaphragm arranged in the path of said light stream.

ERNST FRIEDRICH FISCHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

